Have you never lost half a day of getting work done because Amazon's EC2 API was failing to launch new instances? I have! [1]
To simply hand wave away hosting your own hardware as infeasible and more costly (especially when it's been proven to be more costly) is unproductive at best.
[1] https://hn.algolia.com/?query=AWS%20outage&sort=byPopularity... (HN search of "AWS Outage")